Quarter wave retarder

Crystalline materials with precisely known birefringences are normally used for this purpose, with mica being commonly used. It is difficult, however, to machine most bi-refringent crystals so that a retardation of precisely rc/2 is produced. This is because the thicknesses of the crystal calculated using equaiton (9.1) may be too thin to be practical. Instead, multiple ordered quarter-wave plates can be fabricated with retardation, 8 = 2nj + n/2, where j = 1,2,3,... If a single-order quarter-wave retardation is required, this can be achieved by combining two multiple-order quarter-wave plates of retardation 8 = 2nj + k/2 and 8 = 2nj + jt + n/2, at a relative orientation of 90°. 

Figure 9.4 (a) Fresnel rhomb for quarter-wave retardation, (b) Double Fresnel rhomb... 

Fig. 6.3-5 shows the spectra taken with a CdSe calibration plate on a Bruker IF.S-66 FT-IR spectrometer. Theoretically four curves should result. For calibration purposes, however, it is only necessary to record two curves, as the two other curves are mirror images of the latter. The curves shown in the figure were taken with only a single orientation of the CdSe calibration plate, but one with parallel and another with crossed polarizers. They are the results of 32 coadded interferograms transformed without apodization. As result we chose a power spectrum, since this is less noisy. A further advantage is that we do not need to use the (in the case of calibration spectra) complicated phase correction. The curves cross at certain points. Interpolating between those crossings, we get a curve with which we can multiply our spectra for the correction of Bessel function dependance. We also clearly can identify the node of the Bessel function at about 2450 cm . The modulator was tuned to quarter wave retardation at 1111 cm. ... 

The system described here is based on the principles of ellipsometry (47). Figure 8 gives a block diagram of our experimental setup. The Psi-meter consists of a 2 mW helium-neon polarized laser source, a quarter wave retardation plate to generate circularly polarized light, a synchronously rotating polarizer to... 

Figure 1 Block diagram of a typical electrical birefringence apparatus using either square-pulse (for transient electrical birefringence) or oscillating field (for dynamic electrical birefringence) perturbations. P, polarizer A, analyzer A/4, quarter-wave retardation plate P.S., power supply P.M.T., photomultiplier tube HP-214A, wave-form generator. (Reprinted with permission from Ref. 41. Copyright 1994 American Chemical Society.)...

In a similar fashion, we can tailor the thickness to give a quarter wave retardation of r=71/2. Such a wave plate is useful for converting to and from circularly polarized light. For a quarter wave plate with its fast axis aligned to the y axis (y/=0), the Jones matrix will be... 

The TTL pulses are analysed by a photon counter using the reference signal at frequency f to direct the pulses into two separate counters. The time dependence of the phase shift imparted by the PEM is such that it is exactly quarter-wave retarding or advancing only at the maximum or minimum of the periodic oscillation. For this reason, it is common to select finite time-windows centred at the peak of the modulation cycle for the counting of photon pulses, and not to count the pulses in the dark interval. Even... 

The polarimeter designed and constructed by the University of Hertfordshire, consists of a module containing an aduomatic half (or quarter) wave retarder, which can be stepped to set angular positions. The module is placed upstream of IRIS, the observatory near infrared camera, in which a magnesium fluoride Wollaston prism is used as an analyser (see Figure 1). A focal plane mask, within IRIS, serves to blank out half the fleld so that the e-and o-rays from the Wollaston prism do not overlap when imaging extended objects. 

Figure 5.23 The effect of different cell gaps for the transmissive and the reflective subpixels together with an additional quarter-wave retardation film for the transmissive part. The upper picture is the off-state, the lower the on -state (the LC layer keeps the polarization state of the light for sufficiently high voltage). The transmissive part is two times thicker than the reflective part The LC layer has phase retardation A./4 in the reflective part and X/2 in the transmissive part...

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